WASTEWATER CHLORINATION DECHLORINATION MONITORING AND CONTROL PILOT DEMONSTRATION AT CLARKSON AND CITY OF GUELPH ONTARIO WWTPs Wei Zhang1, Jeremy Leverence1, Jim Nardi2, George Terry2, Scott Kahle1, Matthew Nicolak3 April 11, 2016 At WEAO 2016 Technical Conference Niagara Falls, Ontario, Canada 1 – ASA Analytics, 2 – Ontario Clean Water Agency, 3 – Metcon Sales & Engineering

Acknowledgement City of Guelph Wastewater Treatment Facility was pleased to provide the environment for the study only. Without such great support, this type of study would be impossible. Any results or conclusions are that of the authors only.

Regulatory limit for total residual chlorine (TRC): 0.02 mg/l; Background 2012 Great Lake Water Quality Control Agreement between US and Canadian government – Chemicals of Mutual Concern; Regulatory limit for total residual chlorine (TRC): 0.02 mg/l; Chlorination/de-chlorination disinfection is still widely used; Two critical process conditions: (1) sufficient chlorine concentration at the end of contact chamber to maintain required Disinfectant CT Value; and (2) sufficient de-chlor chemical dosage to control TRC of 0.02 mg/l. Common practice for dosing control: Direct Chemical Analysis - Chlorine and Sulfite Analyzers ORP Automation Monitor residual sulfite as a surrogate to chlorine Adjustment of set point by periodical grab sample

Goal of Pilot Demonstration Demonstrate an ultra-low chlorine analyzer and sulfite analyzer suitable for chemical dosing control while meeting TRC requirement; Evaluate analyzer maintenance, reliability, and accuracy; Evaluate potential chemical saving

ChemScan mini- Analyzer Single sample line, single parameter mini-LowChlor: 0.006 – 2.000 mg/l as Cl2 at final discharge mini-Dechlor: 0.01 – 4.00 mg/l de-chloration as SO3 Accuracy 2% of value or 2x detection limit (whichever greater) Sample Locations Cl2: secondary clarifier effluent, chlorine contact chamber outlet; SO3: final effluent Validation Using potassium permanganate (KMnO4), chemistry is stable then chlorine

Phase I Pilot Demonstration at Clarkson WWPT

Preliminary Conclusions Analyzer is reliable, responsive to low level chlorine Analyzer is low maintenance Co-existence: chlorine and sulfite, but at under 10 sec reaction time. Need further test at longer reaction time Need stable ultra low concentration data at 0.02 mg/l Need Lab comparison runs Complete chlorine analyzer validation Developing in-sample-line cleaning system

Phase II Pilot at Guelph WWTF Analyzer performance in comparison with lab test and ORP probe Build a simulation loop allowing variable reaction time runs. Ultra low (0.02 mg/l) chlorine data and accuracy validation. Upgrading the automatic cleaning system to eliminate the chlorine demand in the sample line. Discover the optimum chlorine and sulfite dosage Determine the potential chemical savings

Chlorine Data at Contact Chamber Outlet

Ultra Low Chlorine Performance Test

Ultra-Low Chlorine Validation Test Unstable nature of chlorine in water; potassium permanganate (KMnO4) is adopted as a substitute for the validation test; Started with 2.0 mg/l stock solution of KMnO4, make 1 liter each of various 0.2, 0.02, 0.01 mg/l standard solution via a serial dilution; Validate analyzer reading through each standard solution; Accuracy: 2 times detection limit or 2% reading whichever greater.

Low Chlorine Validation Validation Test (May 14, 2015 Waukesha, Wisconsin) 0.2 ppm solution run: run 1 = 0.217, run 2 = 0.204, run 3 = 0.203; Average = 0.208 2x LDL = 0.006 ppm x 2 = 0.012 ppm, 2% reading = 0.0042 ppm Accuracy range: 0.2 ppm ± 0.012 = 0.188 ~ 0.212 ppm 0.02 ppm solution run: run 1 = 0.008, run 2 = 0.007, run 3 = 0.008; Average = 0.008 ppm 2x LDL = 0.006 ppm x 2 = 0.012 ppm, 2% reading = 0.0002 ppm Accuracy range: 0.02 ppm ± 0.012 = 0.008 ~ 0.032 ppm. 0.01 ppm solution run: run 1 = 0.005, run 2 = 0.004, run 3 = 0.005; Average = 0.005 ppm 2x LDL = 0.005 ppm x 2 = 0.012 ppm, 2% reading = 0.0001 ppm Accuracy range: 0.01 ppm ± 0.012 = 0.00 ~ 0.022 ppm.

Ultra Low Chlorine Validation Analyzer Validation (July 22, 2015 Guelph WWTP, Ontario) 2.0 ppm solution run: run 1 = 2.006, run 2 = 2.031, run 3 = 0.2.043; Average = 2.027 2x LDL = 0.006 ppm x 2 = 0.012 ppm, 2% reading = 0.041 ppm Accuracy range: 2.0 ppm ± 0.041 = 1.959 ~ 2.041 ppm 0.01 ppm solution run: run 1 = 0.013, run 2 = 0.005, run 3 = 0.003; Average = 0.007 ppm 2x LDL = 0.005 ppm x 2 = 0.012 ppm, 2% reading = 0.0001 ppm Accuracy range: 0.01 ppm ± 0.012 = 0.00 ~ 0.022 ppm.

Simulation Loop set-up

Potential Chemical Savings Chemical dechlorination process can be difficult to control when near zero levels of residual chlorine are required; Conservative dosing of the chemicals to meet discharge limitation is not an uncommon occurrence with existing practices; The following hypothetical calculations are based on a flow rate of 25 MLD treatment plant to illustrate potential chemical savings: Chlorination: 12% liquid sodium hypochlorite at $0.2 per liter Dechlorination: 38% liquid sodium bisulfite at $0.4 per liter Theoretically, by cutting 1 mg/l chlorine and 1 mg/l sulfite from the dosing, results point to the opportunity to save $15,980 per year on sodium hypochlorite and $12,490 on sodium bisulfite per year, i.e., total $28,470 per year.

Conclusion A chlorine analyzer demonstrated accurate and reliable measurement at ultra-low level measurement. A sulfite analyzer demonstrated much improved accuracy and reliability over current bench test and provided a direct measurement over indirect probe reading. The analyzer data and ORP data show some similar trending, but ORP data doesn’t respond to the true chlorine and sulfite variation. Co-exist of chlorine and sulfite in wastewater is clearly observed through series of test runs. Therefore, using trace level sulfite only as an indicator of non-exist chlorine may not be the best practice. Residual sulfite needs to be precisely monitored and controlled. At the City of Guelph, maintaining a 0.2 – 0.4 mg/l SO3 operational range is suggested to keep total residual chlorine less than 0.02 mg/l range. Chemical Saving can be achieved by applying a reliable and accurate chlorine ultra low chlorine and sulfite analyzer.